Exercise training is popular both in normal individuals and in patients with atherosclerotic heart disease. In patients with heart disease the common occurrence of coronary collateral vessels supplying potentially ischemic areas of the myocardium is well documented. The factors controlling flow through these collaterals at rest and during exercise and the effect fo exercise training upon these vessels as well as upon the native coronary circulation and other regional circulations are presently not well defined. Therefore, the aims of the present study are to utilize a dog model with and without chronic collateral formation induced by ameroid constriction of the circumflex and in some cases of the right coronary arteries. Coronary and regional blood flow to other organs will be measured with radioactive microspheres. The hemodynamics of coronary collateral vessels will be investigated by measuring the pressure differential across these vessels with catheters distal to the occluded and in non-occluded vessels and relating this gradient to the mean blood flow. Thus, the hemodynamics of developing and chronic mature coronary collateral vessels will be evaluated with regard to extrinsic neural reflex and intrinsic vasodilatory control mechanisms. Also, the effect of exercise training upon myocardial oxygen consumption as well as collateral and native coronary function and function of other regional circulations will be evaluated. The results from these studies will provide valuable information on the function and mechanisms controlling flow through mature and developing coronary collateral vessels as well as the effect of exercise training on the myocardial and other regional circulations.